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  • Scratching Head....

    Finished building first small system, something not right. Need some knowledge, system consist of..
    4 x 100 watt panels 12v
    40 amp charge controller
    2 x 35 ah deep cycle agm in parrelell
    1000 watt modified sine wave inverter

    Batteries topped off and floating, but as soon as I put a load voltage starts to plummet on the system. I've been using just my tv only that draws 300 watts, don't know what's going on. Any ideas???

  • #2
    Your batteries are damaged from being wired in parallel, and inadequately charged by solar. you should have purchased a 70 amp hour battery or went with a 24 volt setup. You should also have an alternative charger, preferably a smart charger you plug into the Wall or a gen set.
    4X Suniva 250 watt, 8X t-105, OB Fx80, dc4812vrf

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    • #3
      also inverter way too big for 2 X 35 amp hr batteries. I bet you killed the batteries with that inverter, under size wire and cheap terminals. Do you have grid power? AGM batteries? Wall charger? smart charger?
      4X Suniva 250 watt, 8X t-105, OB Fx80, dc4812vrf

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      • #4
        1. They are AGM. Why would it damage them to parallel them?
        2. I do have grid power, and I do have trickle chargers and larger chargers. But the whole point is to use less grid power.
        3. I have a 1000w modified sine wave as well as a 500w pure sine wave, they both had the same results.
        4. I'm using 4x 100w panels, I believed that was decent..... I plan on adding 2 more in a couple of weeks for 600w total.
        5. My cables are 4g and 3', I believed that was decent as well....

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        • Logan005
          Logan005 commented
          Editing a comment
          Unless great care is taken and even then, installing and maintaining parallel batteries, charge and discharge unevenly damaging one or both batteries in short order. Those two 35ah batteries will only power that PS 500 watt inverter for a short time, the 1000 is way over sized for your system. AGM batteries are not serviceable and will only last 300 to 500 cycles under the most ideal conditions. sitting in an over discharged state waiting for inadequate solar array to recharge them, damages the batteries very quickly. If you value your batteries, you should get them on a stiff bulk charge until they go into float, then let the solar maintain them for you. Also keep in mind, many inverters set their LVD=low voltage disconnect way too low. 11.2 volts and lower, therefore damaging your batteries. You should discontinue any load that takes your batteries to a resting state of 12.0 volts or less. If you have grid avail, just use a good smart charger to top them off every other day or so or when you use more power than your array can recover from. Batteries are expensive for the amount of power they provide. inadequate solar makes them even more expensive due to frequent replacement. as often as frequent as 18 to 24 months on a cyclical off grid system. Grid power averages 11 to 22 cents per KWH, a cyclical solar battery system will cost 5 to 10 times that forever.

      • #5
        To use less grid power, you install a proper grid tie system, and charge your back up batteries from the wall outlet.
        4X Suniva 250 watt, 8X t-105, OB Fx80, dc4812vrf

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        • #6
          uscgsapper1, you are right, nothing wrong with your parallel setup or the size of the inverter. I think your 35AH batteries are just too small for the load. At 12 volts you are drawing 25 amps for the TV from 35 AH batteries. I am having a similar predicament. I am running a 600w AC from 4 x 100w batteries wired as 24v and I see a vast voltage drop and the 4 x 160 watt panels are not keeping up with the current.

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          • #7
            I live in a boat, so doin a grid tie is not an option. We have 3 more years left on our plan to buy a farm in the country, this project is for me to start learning and hopefully have the basics figured out before I move and want to build a large system. The small batteries were moved over from my first project which was a mobile solar generator in a tool box on wheels which worked flawlessly. I had an idea they might not handle what I'm asking them to do, but the biggest thing that confuses me right now is why at full sunlight why 400w of panels won't power a 300w tv without even touching the batteries much less destroy them in the matter of minutes!

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            • #8
              What's the charge controller? PWM or MPPT? Can you monitor the volts & amps coming in from the panels? I have a Tracer 4215 with an MT50 monitor and I am only getting about 100 watts per panel out of my 160 watt panels. Still don't know why. Checked each panel and they are putting out close to 160 in full sun.

              As far as battery goes, you and I are close.. you're running 300w off of 70AH @ 12v and I'm running 600w off of 200AH @ 24v. So unless anyone else has some wisdom to inject here, I'd say our battery banks are vastly under sized. Still, I was hoping the panels would compensate since I only run my A/C when panels are in full sun.

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              • #9
                Originally posted by uscgsapper1 View Post
                Finished building first small system, something not right. Need some knowledge, system consist of..
                4 x 100 watt panels 12v
                40 amp charge controller
                2 x 35 ah deep cycle agm in parrelell
                1000 watt modified sine wave inverter

                Batteries topped off and floating, but as soon as I put a load voltage starts to plummet on the system. I've been using just my tv only that draws 300 watts, don't know what's going on. Any ideas???
                So what is the problem other than operator error. Your system was designed to fail.

                A 300 watt load draws 25 amps. You cannot draw 25 amps from a 70 AH battery for more than a hour before the voltage sags and your Inverter shuts itself off. You should not be using parallel batteries especially at TOY sizes you are running. There is no reason to run parallel batteries ever.

                A 1000 watt Inverter using AGM batteries requires a minimum 12 volt 400 AH battery. All you have is 70 AH. Even a 400 AH battery is small as at 1000 watts only gives you 90 minutes run time. A 12 volt 400 AH battery needs a 750 watt minimum panel wattage with a 60 amp MPPT controller.

                Based on your panel wattage of 400 watts the minimum size battery you should be using is 12 volt 300 AH Flooded or 150 AH AGM with a 500 watt Inverter. However even that can only run a 300 watt load 5 hours with FLA or 2 hours AGM.

                Nothing you have is made to do what you want to do. In short you planned to fail from the start. In the end you failed to plan, so your plan failed.
                Last edited by Sunking; 06-25-2016, 12:22 PM.
                MSEE, PE

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                • #10
                  good luck with the solar and the upcoming farm project.

                  First thing that caught my eye was your TV draw. 300 watts? I think you can get an massive energy efficient TV that draws 1/6th of that.
                  the killer is the dish network box - mine draws more "turned off" than the TV on - I cut the power completely to it when not in use.



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